Editing Reaction wheel (section)

== Failures and mission impact ==

The failure of one or more reaction wheels can cause a spacecraft to lose its ability to maintain attitude (orientation) and thus potentially cause a mission failure. Recent studies conclude that these failures can be correlated with [[space weather]] effects. These events probably caused failures by inducing electrostatic discharge in the steel [[ball bearing]]s of [[Ithaco]] wheels, compromising the smoothness of the mechanism.<ref>W. Bialke, E. Hansell "[http://esmats.eu/esmatspapers/pastpapers/pdfs/2017/bialke.pdf A Newly Discovered Branch of the Fault Tree Explaining Systemic Reaction Wheel Failures And Anomalies]", 2017</ref>  Supporting this hypothesis, newer reaction wheels have non-conducting ceramic bearings, and none have failed in this manner.

Two servicing missions to the [[Hubble Space Telescope]] have replaced a reaction wheel. In February 1997, the Second Servicing Mission ([[STS-82]]) replaced one<ref name="Hubblesite, RW" >{{cite web  |url=http://hubblesite.org/the_telescope/team_hubble/servicing_missions.php    |title=Team Hubble: Servicing Missions -- Servicing Mission 3B   |quote=Astronauts replaced one of the four Reaction Wheel Assemblies that make up Hubble's Pointing Control System. }}</ref> after 'electrical anomalies', rather than any mechanical problem.<ref name="Carre, Bertrand, 1999" >{{Cite journal  |title=Analysis of Hubble Space Telescope Reaction Wheel Lubricant  |year=1999  |journal=Journal of Spacecraft and Rockets  |last1=Carré  |first1=D. J.   |last2=Bertrand  |first2=P. A.   |volume=36  |issue=1  |doi=10.2514/2.3422   |pages=109–113 |bibcode=1999JSpRo..36..109C}}</ref> Study of the returned mechanism provided a rare opportunity to study equipment that had undergone long-term service (seven years) in space, particularly for the effects of vacuum on [[vacuum lubricant|lubricant]]s. The lubricating compound was found to be in 'excellent condition'.<ref name="Carre, Bertrand, 1999" /> In 2002, during Servicing Mission 3B ([[STS-109]]), astronauts from the shuttle [[Space Shuttle Columbia|''Columbia'']] replaced another reaction wheel.<ref name="Hubblesite, RW" /> Neither of these wheels had failed and Hubble was designed with four redundant wheels, and maintained pointing ability so long as three were functional.<ref>{{cite web | url = http://www.spacetelescope.org/about/general/gyroscopes/ | title = Gyroscopes | publisher = ESA | access-date = 8 April 2016}}</ref>

In 2004, during the mission of the ''[[Hayabusa]]'' spacecraft, an X-axis reaction wheel failed. The Y-axis wheel failed in 2005, causing the craft to rely on chemical thrusters to maintain attitude control.<ref>{{cite web|url=http://science1.nasa.gov/missions/hyabusa/|title=Hayabusa|publisher=[[NASA]]|access-date=May 15, 2013|url-status=dead|archive-url=https://web.archive.org/web/20130601154943/http://science1.nasa.gov/missions/hyabusa/|archive-date=June 1, 2013}}</ref>

From July 2012 to May 11, 2013, two out of the four reaction wheels in the [[Kepler space telescope]] failed. This loss severely affected Kepler{{'s}} ability to maintain a sufficiently precise orientation to continue its original mission.<ref>{{cite web  |url=https://news.yahoo.com/planet-hunting-kepler-spacecraft-suffers-major-failure-nasa-203147459.html  |title=Planet-Hunting Kepler Spacecraft Suffers Major Failure, NASA Says  |author=Mike Wall  |publisher=[[Space.com]]  |date=May 15, 2013  |access-date=May 15, 2013}}</ref> On August 15, 2013, engineers concluded that Kepler's reaction wheels cannot be recovered and that planet-searching using the transit method (measuring changes in star brightness caused by orbiting planets) could not continue.<ref name="NASA-20130815">{{cite web |url=http://www.nasa.gov/content/nasa-ends-attempts-to-fully-recover-kepler-spacecraft-potential-new-missions-considered/ |title=NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered |date=August 15, 2013 |access-date=August 15, 2013 |archive-date=September 7, 2018 |archive-url=https://web.archive.org/web/20180907235849/https://www.nasa.gov/content/nasa-ends-attempts-to-fully-recover-kepler-spacecraft-potential-new-missions-considered/ |url-status=dead }}</ref><ref name="NYT-20130815">{{cite news |last=Overbye |first=Dennis |title=NASA's Kepler Mended, but May Never Fully Recover |url=https://www.nytimes.com/2013/08/16/science/space/nasas-kepler-mended-but-may-never-fully-recover.html |date=August 15, 2013 |work=[[New York Times]] |access-date=August 15, 2013}}</ref><ref name="SP-20130815">{{cite web |last=Wall |first=Mike |title=Planet-Hunting Days of NASA's Kepler Spacecraft Likely Over |url=http://www.space.com/22387-nasa-planet-hunting-kepler-spacecraft-problems.html |date=August 15, 2013 |work=[[Space.com]] |access-date=August 15, 2013}}</ref><ref>{{cite news |title=Kepler: NASA retires prolific telescope from planet-hunting duties |work=BBC News|date=16 August 2013|url=https://www.bbc.co.uk/news/science-environment-23724344}}</ref> Although the failed reaction wheels still function, they are experiencing friction exceeding acceptable levels, and consequently hindering the ability of the telescope to properly orient itself. The Kepler telescope was returned to its "point rest state", a stable configuration that uses small amounts of thruster fuel to compensate for the failed reaction wheels, while the Kepler team considered alternative uses for Kepler that do not require the extreme accuracy in its orientation needed by the original mission.<ref>{{cite web|last=Hunter|first=Roger|title=Kepler Mission Manager Update: Pointing Test Results|url=http://www.nasa.gov/content/kepler-mission-manager-update-pointing-test-results/#.UkFN8j_DOdk|work=NASA.gov|publisher=NASA|access-date=24 September 2013}}</ref> On May 16, 2014, NASA extended the Kepler mission to a new mission named [[Kepler space telescope#Second Light .28K2.29|K2]], which uses Kepler differently, but allows it to continue searching for [[exoplanets]].<ref name="NASA-20140516">{{cite web |url=http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |title=Kepler Mission Manager Update: K2 Has Been Approved! |work=nasa.gov |date=May 16, 2014 |publisher=[[NASA]] |access-date=May 17, 2014 |others=NASA Official: Brian Dunbar; Image credit(s): NASA Ames/W. Stenzel |first=Charlie |last=Sobeck |editor1-first=Michele |editor1-last=Johnson |archive-url=https://web.archive.org/web/20140517191944/http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |archive-date=May 17, 2014 |url-status=live }}</ref> On October 30, 2018, NASA announced the end of the Kepler mission after it was determined that the fuel supply had been exhausted.<ref>{{Cite news|url=https://www.nasa.gov/press-release/nasa-retires-kepler-space-telescope-passes-planet-hunting-torch|title=NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch|last=Chou|first=Felicia|date=2018-10-30|work=NASA|access-date=2018-11-16|language=en}}</ref>

The NASA space probe ''[[Dawn (spacecraft)|Dawn]]'' had excess friction in one reaction wheel in June 2010. It was originally scheduled to depart Vesta and begin its two-and-a-half-year journey to Ceres on August 26, 2012;<ref name=Dawn-2012-08/> however, a problem with another of the spacecraft's reaction wheels forced ''Dawn'' to briefly delay its departure from Vesta's gravity until September 5, 2012, and it planned to use thruster jets instead of the reaction wheels during the three-year journey  to Ceres.<ref name=Dawn-2012-08>{{cite web |url=http://dawn.jpl.nasa.gov/feature_stories/engineers_assess_reaction_wheel.asp |title=Dawn Engineers Assess Reaction Wheel |publisher=NASA{{\}}Jet Propulsion Laboratory |first=Jia-Rui C. |last=Cook |date=August 18, 2012 |access-date=January 22, 2015 |archive-url=https://web.archive.org/web/20150315131809/http://dawn.jpl.nasa.gov/feature_stories/engineers_assess_reaction_wheel.asp |archive-date=March 15, 2015}}</ref> The loss of the reaction wheels limited the camera observations on the approach to Ceres.

On the evening of Tuesday, January 18, 2022, a possible failure of one of the [[Swift Observatory]]'s reaction wheels caused the mission control team to power off the suspected wheel, putting the observatory in safe mode as a precaution. This was the first time a reaction wheel failed on Swift in 17 years. Swift resumed science operations on February 17, 2022.<ref>[https://swift.gsfc.nasa.gov/news/2022/safe_mode.html?linkId=148869038 NASA's NASA's Swift Observatory Returns to Science] NASA News, February 18, 2022, NASA. Retrieved April 16, 2023</ref>